The major components of the flue gas desulfurization byproduct from thermal power plants and facilities (briefly referred to as FGD byproduct) are gypsum (CaSO4.2H2O) or a mixture of gypsum and calcium sulfite (CaSO3). The byproduct further contains a certain amount of powder coal ash and water. Relatively pure calcium sulfate (gypsum) is common building material; while, the calcium sulfite is waste, and because of its instability, it is easy to induce secondary pollution to the environment. In fact, because China is rich in natural gypsum, the price is not high; and it is not necessary to directly use gypsum that contains a lot of water, ash and impurity, generated from flue gas desulfurization as building gypsum, because that will cost so much, that is, the FGD byproduct only can be used after being further refined and dehydrated. Therefore, there is no competitive power on the market in China for flue gas desulfurization byproduct used as building gypsum. Only a little of it is used as cement additives. Most of it is thrown away as waste.
At present, the methods for electric power plants to treat the FGD byproduct chiefly are landfill, storage in ash storage pool and the like. However, when disposing of 10 thousand tons of the desulfurization byproduct, a fossil-fuel power plant needs to takeover about 200 m2 of land, and it costs 2.5 to 10 thousand US dollars for operating the ash field, and 2.5˜6.75 thousand US dollars for ash transportation. So, from the aspect of environmental protection or from the aspect of economy, the effective use of the FGD byproduct is a subject that needs to be studied.
At present, there are mainly four aspects for alkali soil amelioration, which are water conservancy amelioration methods (irrigation, drainage, warping, rice planting, anti seepage and the like), agriculture amelioration methods (land level off, cultivation improvement, use of alien earth, fertilization, insemination, crop rotation, inter-planting and the like), biology amelioration methods (halophyte and grazing planting, green manure fertilization, tree planting and the like), and chemistry amelioration methods (the application of improver-additives, such as gypsum, phosphor gypsum, calcium sulfite and the like).
When using gypsum to ameliorate soil, HE Dixin (he used pure gypsum not the FGD byproduct for alkali soil amelioration. See, the Formation and Amelioration of Alkali Soil, 1980) calculated the application amount mainly consider the difference value generated from exchangeable sodium subtracting 5% or 10% of alkalization degree as the reference for gypsum application amount. Regarding Na2CO3 and NaHCO3, they were taken into the application amount when their amount were too much, while they were ignored when their amounts were so less. Moreover, there was no consideration for the exchangeable magnesium in the calculation. Therefore, the calculated application amount was less than the amount needed in factual amelioration, which would affect the effect of amelioration.